1. Field of the Invention
The present invention relates generally to bicycle type wheels and especially to such wheels including tensioned spokes connecting a rim to a hub. More specifically, the invention relates to front and rear, radially and tangentially laced, tensioned spoke wheels comprising a hub, a rim and a plurality of spokes connecting the rim to the hub, and a mechanism for attaching the spokes at the rim to reduce spoke stresses and breakage and/or rim stresses.
2. Description of the Prior Art
Spoked wheels, especially for bicycles, are laced generally in one of two spoking patterns. Radially spoked wheels, with spokes extending generally radially outwardly from hub flanges, are used as front wheels for bicycles. Tangentially spoked wheels, with spokes extending tangentially or nearly so, relative to the hub flanges, are used as rear bicycle wheels. In both cases, the longitudinal axis of a spoke deviates from a radial orientation relative to the intersection of the center plane of the wheel and the rotational axis of the wheel. This is illustrated in FIGS. 5 and 6, which are based upon FIGS. 2 and 1, respectively, of U.S. Pat. No. 4,583,787 (xe2x80x9cMichelottixe2x80x9d), the disclosure of which is incorporated herein by reference.
FIG. 5 illustrates what we will call the centering angle of a spoke, in the context of a rim 10 which has a radius R. In the drawing, the radius R coincides with the center plane of a wheel including the rim 10, the center plane being perpendicular to the axis of rotation of the wheel and intersecting the center line of the rim. The longitudinal axis, designated SA, of a spoke (not shown) attached to a left hub flange (not shown) deviates from the rim radius R by an angle designated CA for centering angle. In the drawing, the spoke axis SA intersects the rim radius R outside of the rim 10. Because of this deviation, a spoke connected to the rim 10 and a left hub flange (not shown) exerts a lateral force which is balanced, more or less, depending on the spoking pattern, by an opposite lateral force exerted by a spoke (not shown) connected to the rim 10 and a right hub flange (not shown). These lateral forces keep the rim centered in the wheel center plane and provide essential lateral stability to radially spoked wheels and to tangentially spoked wheels. Thus, the name centering angle.
FIG. 6 illustrates what we will call the torsional angle of a spoke, in the context of a rim 12 which has a radius R. In the drawing, the radius R coincides with the center plane of a wheel including the rim 12, the center plane being perpendicular to the axis of rotation of the wheel and intersecting the center line of the rim 12. The longitudinal axis, designated SA, of a spoke 14 attached to a right or left hub flange (not shown) deviates from the rim radius R by an angle designated TA for torsional angle. Because of this deviation, which is found in tangentially spoked wheels, primarily used as rear driving wheels, the spoke is operable to transmit a pulling or torsional force from a rotating hub to the rim 12, tending to cause the rim to rotate. Thus, the name torsional angle. Generally speaking, there is no torsional angle in wheels which are radially spoked.
If it were not for the torsional and centering angles of spokes, securing them to a rim would be a fairly simple matter. It is, however, a complicated matter to secure spokes to a rim. This is further complicated because the centering angle and the torsional angle are not constant in bicycle wheels on a moving bicycle. The weight of a rider, forces associated with turning, forces associated with braking and forces associated with acceleration, among other things, can and do cause small but not insignificant changes in these angles and these changes occur very rapidly during cycling. These angle changes cause stresses in spokes, particularly where they are fastened to the rim, typically by internally threaded nipples. Various attempts to deal with these stresses are discussed below.
The Michelotti patent discloses a bush which is received in a spoke bore in a rim. The bush is configured with two cylindrical co-axial bodies for receiving the conical head and the cylindrical section of an internally threaded nipple which receives the threaded end of a spoke. The bush is further configured to minimize deviation between the common axes of the cylindrical bodies and the longitudinal axis of the spoke. Apart from difficulties associated with properly orienting the bushes to achieve the desired result, this approach does not begin to account for dynamic changes in the centering angle and the torsional angle.
Another prior art method is illustrated in FIG. 2 which shows a rim 20, in cross-section and a spoke 22 connected to the rim 20. The rim 20 has a rounded spoke bed indicated at 24 which is raised, as indicated at 26, adjacent to sidewalls 28 of the rim 20, and lower in the middle, as indicated at 30. A spoke bore, indicated at 32, has an axis which is oriented, so far as possible, to coincide with the longitudinal axis of the spoke 22, taking into account the centering angle as well as the torsional angle, if any, of the spoke 22. A nipple 34 is internally threaded and is attached to a threaded end 36 of the spoke 22. Portions of the bottom end 38 of the nipple 34 engage the rounded rim floor 24 while other portions of the bottom 38 of the nipple 34 do not engage the rim floor 24. This condition is exacerbated under dynamic conditions when the centering angle and the torsional angle are changing. The resulting stresses tend to concentrate in the unthreaded portion of the spoke 22, immediately adjacent to the threaded portion 36.
Referring now to FIGS. 3 and 4, an extended nipple 40, similar to the nipple shown in the Michelotti patent with a head 6, has a head 42 which is seated on a substantially flat rim floor 44 of a rim 45. As can be seen in FIG. 4, however, only a small portion of the underside 46 of the head 42 of the nipple 40 seats against the rim floor when it engages a spoke 47 extending through the rim 45. In this arrangement, the spoke hole, indicated at 48, is inclined so that its axis coincides generally with the longitudinal axis of the spoke, taking into account the centering angle and, if necessary, the torsional angle. The nipple 40 has a slot, indicated at 49 in FIG. 4, which is engageable by a screwdriver or the like to properly tension the spoke 47.
Bicycle wheel rims encounter large stresses at spoke locations. Typically, a spoke extends through a spoke hole in the rim and is connected inside of the rim to an internally threaded nipple. Low spoke count wheels, i.e., in the range of 14 or 16 spokes up to 20 or 24 spoke wheels have higher spoke tensions than conventional wheels with 28 or more spokes. Consequently, low spoke wheels have a higher stress concentration where the spokes are connected to the rim than conventional wheels because each spoke must carry a higher load when there are fewer spokes so that the total tension in the spokes which centers the rim and the hub within the rim is about the same as in a higher spoke wheel. Some have undertaken to reinforce and/or reduce rim weight while providing adequate strength at spoke connection points, in rather remarkable ways. EP 0 715 001 A1 discloses the idea of extruding a rim section having a spoke bed of a given thickness, masking spoke connection points and chemically removing material from the rim except under the masks, resulting in a rim with thickened portions coinciding with spoke connection points and reduced thicknesses elsewhere on the rim. U.S. Pat. No. 6,402,256 B1 discloses a rim that is made from a rim section having a spoke bed with a given thickness and the mechanical removal of spoke bed material in between the spoke connection points. This produces a rim that is reinforced at spoke connection points.
The present invention is based upon the discovery of an improved method for attaching a threaded end of a spoke to a rim and a wheel made in accordance with the method. According to the method, a rim, preferably one having a substantially flat rim floor, is provided with spoke bores that are oriented so that the axis of the bore coincides or is substantially parallel to a radius of the wheel. The threaded end of the spoke is inserted through the spoke bore, a cylindrical spacer element is positioned around the spoke end and an internally threaded nipple is attached to the threaded portion of the spoke end. According to the method, the spacer height is controlled, relative to the stiffness of the spoke, so that, when the spoke is tightened, the threaded portion and an unthreaded portion adjacent thereto coincide with or are substantially parallel to a radius of the wheel and so that a bend is formed in the spoke, as it is tightened, to accommodate centering angle and, if necessary, the torsional angle. The bend is formed in the spoke at a point which is remote from the transition between the threaded portion of the spoke and the adjacent, unthreaded spoke portion. Preferably, the bend is formed at or near a point on the spoke, adjacent to point where the spoke exits the underside of the rim. This arrangement moves stresses of the type described above, away from the transition between the threaded portion of the spoke and the unthreaded portion of the spoke, while providing for a firm, stable support between the underside of the nipple and the spoke bed with good distribution of tensile stresses on the rim floor.
In a preferred embodiment of a wheel according to the present invention, a spoke from the left side of the hub flange is paired, at the rim, with a spoke from the right side of the hub flange, and a spacer comprising a spoke plate is positioned between the spoke bed and the nipples, inside of the rim. The length of the spoke plate is greater than the distance between the spokes of a pair, at the rim, and coaction between the spoke plates and the nipples, on the one hand, and between the spoke plate and the rim spoke bed, on the other hand, distributes the load associated with the tensioned spokes over a substantial portion of the spoke bed, thereby eliminating the high pressure point loading of the spoke bed around each spoke hole and eliminating the need to reinforce or bolster the spoke bed at spoke connection points through chemical or mechanical means. Advantages accrue with the use of a spoke plate even if it does not result in a bend in the spoke remote from the thread onset. In one embodiment, the spoke holes in the spoke plate are surrounded with a socket shaped depression and the end of a nipple that engages the spoke plate is rounded as a ball so that the nipple aligns itself with the spoke, greatly reducing stresses in the spoke under dynamic conditions.
Accordingly, it is an object of the present invention to provide a method for connecting a spoke to a rim which will reduce stresses found in prior art wheels adjacent to the intersection of the threaded end portion of the spoke and the adjacent, unthreaded portion of the spoke.
It is an object of the present invention to provide a method for connecting a spoke to a rim which will reduce stresses found in rims of prior art wheels adjacent to the spoke.
It is a further object of the invention to provide a method for securing a spoke to a rim with a nipple so that the underside of the spoke nipple is firmly supported relative to the rim floor.
It is a further object of this invention to provide a wheel which resists failure due to bending of the spoke adjacent to the intersection between the threaded end portion of the spoke and the adjacent unthreaded portion.
It is yet another object of the invention to provide a wheel in which an end portion of the spoke is oriented so that its longitudinal axis coincides with or is substantially parallel to a radius of the wheel and there is a bend in a portion of the spoke at a point which is remote from the intersection between the threaded portion of the spoke and the adjacent unthreaded portion.
It is a primary object of this invention to provide an improved spoked wheel.
These and other objects and advantages of the present invention will no doubt become apparent to those skilled in the art after having read this detailed description of the invention including the following description of the preferred embodiment which is illustrated by the various figures of the drawing.